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They stick on using surface tension from a drop of water - IKYN.
See this thread on Yacf for all the info:
https://yacf.co.uk/forum/index.php?topic=83623.0Mine worked OK on the IPWR. The one on the right lens dropped out after a few days but it wasn't strong enough anyway. Right lens is very curved so wasn't surprised it happened. The left one, which I mainly relied on, stayed in all the way.
I have photochromatic lenses in frames that give me good upwards visibility for TT position.
Got them for TCR. Worked well.
Can't read well in them, though. So, for IPWR I got stick-on bifocals. One fell off but one has stayed in place for 2+ weeks on the road. Can read Garmin / phone well with it (with one eye).